1. Field of the Invention
The present invention relates to an image forming device and an image forming method. In particular, the invention relates to an image forming device of a system of transferring a toner image formed on an image support body to a recording medium via an intermediate transfer body and an image forming method using the image forming device.
2. Description of the Related Art
Conventionally, as an image forming method by an image forming device such as a copying machine and a printer using an electrophotographic system, a method is known in which a toner image formed on a photoconductor drum serving as an image support body is once primarily transferred onto an intermediate transfer belt and then the toner image on the intermediate transfer belt is again secondarily transferred onto a recording medium to form an image. It is known that use of this method leads to the advantage that it is possible to suppress transfer failure and generation of a shift of color registration due to many factors such as holding states of recording media and surface properties.
Here, the toner image transferred on the intermediate transfer belt, regardless of the photoconductor drum being a tandem type or a one drum type, is made to pass between the photoconductor drum and the transfer roll of the intermediate transfer belt in a plurality of times. At this time, the surface of the intermediate transfer belt and the toner image are friction charged, the charging amount of the toner on the intermediate transfer belt is varied, and it is revealed that the electrostatic adsorption force between the transferred toner and the intermediate transfer belt is changed. In other words, an electrostatic adsorption force is expected to be generated between the toner and the intermediate transfer belt.
Because of this, it has been found that the electrostatic adsorption force between the toner and the intermediate transfer belt becomes greatly different and the secondary transferarability of the toner image becomes extremely different.
Accordingly, in a resin belt used in color image forming devices of a tandem system, etc, electroconductive seamless belts provided with good strength, particularly good bending durability have been proposed (e.g., Patent Document 1). More specifically, proposed is an electroconductive seamless belt for transferring of a tandem system, in which a recording medium held by electrostatic adsorption is circularly driven by a driving member, and delivered to four kinds of image forming materials, and then each toner image is transferred to the recording medium in order. In this electroconductive seamless belt, a thermoplastic polyamide and a polymer-alloy resin comprising a thermoplastic polyamide and a thermoplastic elastomer are employed. [Patent Document 1] JP2001-350347A (Claims, and FIGS. 2 and 3)
However, in the color image forming device of JP2001-350347A, only the volume resistance of an electroconductive seamless belt is specified and no description is given for surface resistance. Therefore, a toner cannot be effectively transferred to an intermediate transfer belt in some cases. In other words, in some cases, the largest pressurization point of the primary transfer roller to the intermediate transfer belt may be shifted from the largest pressurization point of the photoconductor drum to the intermediate transfer belt. That is, in the case of offset placement, so as not to apply an excessive pressure to the intermediate transfer belt, an electric current needs to be flowed via the surface of the electroconductive seamless belt, and the problem of doing so being difficult is created.
Hence, in the color image forming device of JP2001-350347A, particularly in the case of using a positively charged toner, a problem is posed in that a toner cannot be effectively transferred to the intermediate transfer belt.
Furthermore, where a positively charged toner is used, when a toner transferred on the intermediate transfer belt is made to pass through a primary transfer position in a plurality of times, an outermost surface layer of the toner image transferred on the intermediate transfer belt is affixed to the photoconductor drum and thus peeled. As a result, there is a problem in that coming off of the center of the line image of the toner image on the intermediate transfer belt, i.e., “central fade-out” is liable to occur.